1. Field of the Invention
The present invention relates to a photovoltaic panel including a plurality of photovoltaic elements and a method of producing a photovoltaic cell.
2. Discussion of Related Art
Japanese Patent Document No. 6(1994)-13633 discloses a method of producing a photovoltaic panel. This method includes (a) the step of forming a number of holes in an aluminum foil as an electrically conductive member; (b) the step of fitting, in each of the thus formed holes, a photovoltaic element having P-N junction between a core portion and a shell portion; (c) the first connecting step of pressing, by impact pressing, the photovoltaic elements which have been heated up to 500xc2x0 C. to 577xc2x0 C., into the holes and then cooling those elements down to the room temperature, so that the conductive member is electrically connected to the shell portion of each photovoltaic element; (d) the step of removing one of respective half portions of the shell that correspond to the opposite major surfaces of the conductive member, so that the respective cores of the photovoltaic elements are partly exposed; (e) the step of forming an electrically insulating layer on the exposed portions of the cores of the photovoltaic elements and the corresponding one major surface of the conductive member; (f) the step of polishing portions of the insulating layer covering the cores of the photovoltaic elements, so that the cores are partly exposed and (g) the second connecting step of electrically connecting a second electrically conductive plate-like member to the thus exposed portions of the cores of the photovoltaic elements.
The present invention provides a photovoltaic-panel producing method and a photovoltaic panel which have one or more of the following technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (20). Any technical feature that includes another technical feature shall do so by referring, at the beginning, to the parenthesized sequential number given to the latter feature. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. In addition, in the case where one technical feature recites a plurality of items, it is not essentially required that all of those items be simultaneously employed. That is, it is possible to select and employ only a portion (one, two, . . . , but not all) of those items.
(1) According to a first feature of the present invention, there is provided a method of producing a photovoltaic panel, comprising the steps of forming a plurality of holes in a first electrode plate, fitting, in the plurality of holes, a plurality of photovoltaic elements, respectively, each of which has a P-N junction between a core portion thereof and a shell portion thereof, electrically connecting a first portion of the shell portion of the each photovoltaic element to the first electrode plate, removing one of opposite second portions of the shell portion of the each photovoltaic element that are located on both sides of the first portion of the shell portion, so that a third portion of the core portion of the each photovoltaic element that corresponds to the one second portion of the shell portion is exposed, and electrically connecting the third portion of the core portion of the each photovoltaic element to a second electrode plate, wherein at least one of the step of electrically connecting the first portion and the step of electrically connecting the third portion comprises soldering, with a solder, a corresponding one of the first portion and the third portion to a corresponding one of the first electrode plate and the second electrode plate.
In the present photovoltaic-panel producing method, the electrical connection between each of the photovoltaic elements and at least one of the first and second electrode plates is done by soldering. In contrast, in the first connecting step of the conventional producing method, each photovoltaic element and an electrically conductive member are connected by diffused junction in which two elements are bonded to each other by utilizing the diffusion of atoms occurring at the interface of the two elements. A device for carrying out the diffused junction is expensive, and needs to be used at a high temperature not lower than 500xc2x0 C. Moreover, the diffused junction needs a long time. The soldering, utilized in the present method, does not need an expensive device. In addition, the solder can be molten at a temperature (from 150xc2x0 C. to 300xc2x0 C. depending on sorts) which is considerably lower than a temperature at which the diffused junction is done. Since the solder is easily molten, the electrical connection can be done, by the soldering, in a shorter time. The core portion and shell portion of each photovoltaic element may be connected, either directly or indirectly, to the first and second electrode plates, respectively.
(2) According to a second feature of the present invention that includes the first feature (1), the photovoltaic-panel producing method further comprises forming the each photovoltaic element from a silicon-based material, so that the each element has the P-N junction between the core portion and the shell portion, and forming a to-be-soldered layer from a material having a good capability to be connected to both the solder and the silicon-based material, so that the to-be-soldered layer covers at least the first portion of the shell portion of the each photovoltaic element.
Thus, the to-be-soldered layer is formed from the material having the good capability to be connected to both the solder and the photovoltaic element. This capability can be called as a capability to be connected to metals, or an affinity to metals. The to-be-soldered layer may cover the entire outer surface of each photovoltaic element or a portion of the outer surface of the same. The to-be-soldered layer may be formed by plating. The plating may be either electrolytic plating or chemical (i.e., electroless) plating. Since the chemical plating can be carried out by a cheaper device, it contributes to reducing the production cost of the photovoltaic panel. The material from which the to-be-soldered layer is formed may comprise at least one of nickel, titanium, cobalt, palladium, gold, and silver. A material comprising nickel or titanium is preferable.
(3) According to a third feature of the present invention that includes the second feature (2), the step of electrically connecting the first portion comprises soldering the to-be-soldered layer covering the first portion of the shell portion, to the first electrode plate.
Since the shell portion of each photovoltaic element is soldered to the first electrode plate via the to-be-soldered layer, the shell portion is more easily connected to the electrode plate than the case where the former is directly connected to the latter.
(4) According to a fourth feature of the present invention that includes the second or third feature (2) or (3), the to-be-soldered layer additionally covers the one second portion of the shell portion, and wherein the step of removing the one second portion comprises removing both the to-be-soldered layer covering the one second portion, and the one second portion.
The to-be-soldered layer can be removed by using a plating releasing or removing agent, and the shell portion can be removed by using an etching agent or liquid. The remaining portion of the to-be-soldered layer that is other than the portion thereof to be connected by the soldering, may be removed when the one second portion of the shell portion is removed. It is preferred that the plating removing agent be selected from one of those which are not influential to the solder. For example, a strong acid removing agent is preferable. The etching agent may be selected from strong acids such as sulfuric acid, nitric acid, hydrochloric acid, or hydrogen fluoride. For example, a mixture of nitric acid and hydrogen fluoride is preferably used to remove the shell portion.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the photovoltaic-panel producing method further comprises forming, after the one second portion of the shell portion of the each photovoltaic element is removed and the third portion of the core portion of the each element is exposed, an electrically insulating layer to cover the third portion of the core portion of the each element and at least a portion of one of opposite surfaces of the first electrode plate, and removing the insulating layer covering the third portion of the core portion of the each photovoltaic element, so that the third portion of the core portion is exposed.
The insulating layer is so formed as to cover the exposed, third portions of the core portions of the photovoltaic elements, and respective portions of the insulating layer that are to be connected to the second electrode plate are removed. Since the insulating layer is provided between the first and second portions of each photovoltaic element that are connected to the first and second electrode plates, respectively, respective conductive layers of the first and second electrode plates are reliably insulated. For example, when the core portion of each photovoltaic element is soldered to the second electrode plate, the solder may climb up along the core portion of the each element. Even in this case, the insulating layer can effectively prevent the solder from reaching the conductive layer of the first electrode plate. It is preferred that the insulating layer be highly capable of electrical insulation. If the insulating layer is formed of a material which is highly capable of application, it is easily formed. For example, the insulating layer may be formed of a synthetic resin such as an acrylic resin, a urethane resin, or an epoxy resin. It is preferred that the insulating layer be removed by a mechanical method such as sand blasting. However, it is not essentially required that the insulating layer be formed on the core portion of each photovoltaic element, because, as described later, the first electrode plate may include an insulating layer which insulates the respective conductive layers of the first and second electrode plates from each other.
(6) According to a sixth feature of the present invention that includes the fifth feature (5), the photovoltaic-panel producing method further comprises forming the each photovoltaic element from a silicon-based material, so that the each element has the P-N junction between the core portion and the shell portion, and forming a to-be-soldered layer from a material having a good capability to be connected to both the solder and the silicon-based material, so that the to-be-soldered layer covers the exposed, third portion of the core portion of the each photovoltaic element.
This to-be-soldered layer may be formed from the same material as that from which the to-be-soldered layer recited in the second feature (2) is formed, in the same manner as that in which the latter layer is formed.
(7) According to a seventh feature of the present invention that includes the sixth feature (6), the step of electrically connecting the third portion comprises soldering the to-be-soldered layer covering the third portion of the core portion, to the second electrode plate.
In this photovoltaic panel, the core portion of each photovoltaic element is connected to the second electrode plate via the to-be-soldered layer.
(8) According to an eighth feature of the present invention that includes any one of the first to seventh features (1) to (7), the photovoltaic-panel producing method further comprises forming at least one of the first electrode plate and the second electrode plate, by coating at least a portion of one of opposite surfaces of a substrate with the solder.
The substrate may be an electrically insulating layer formed of a synthetic resin, an electrically conductive layer formed of an electrically conductive material, or the combination of an insulating layer and a conductive layer which are superposed on each other. If the substrate has a high rigidity, the holes can be easily formed by punching. The solder may coat one entire surface of the substrate, or only a certain portion of one surface of the same.
(9) According to a ninth feature of the present invention that includes the eighth feature (8), the step of forming the holes comprises forming the holes such that an area of an opening of each of the holes that opens on the side of the one surface of the substrate that is coated with the solder, is smaller than an area of an opening of the each hole that opens on the side of the other surface of the substrate.
Since the area of opening of each of the holes that opens on the side of the one surface of the substrate that is coated with the solder (hereinafter, referred to as xe2x80x9cthe side of the solder layerxe2x80x9d) is smaller than the area of opening of the same hole that opens on the side of the other surface of the substrate, the step of removing the shell portion can be easily carried out. In addition, a broader area of the shell portion can be removed. If the diameter of the opening of each hole on the side of the solder layer is somewhat smaller than that of each photovoltaic element, then the each element can be reliably fixed, by fitting, to the first electrode plate. In the case where the holes are formed by punching with a punch, it is desirable that the punch be used on the first electrode plate from the side of the solder layer toward the other side. In this case, the area of opening of each hole on the side of the solder layer is naturally made smaller than the area of opening of the same hole that opens on the other side. In addition, the holes are formed with accurate dimensions. Therefore, the photovoltaic elements are advantageously fitted in respective portions of the holes that are located on the side of the solder layer.
(10) According to a tenth feature of the present invention that includes any one of the first to ninth features (1) to (9), the step of electrically connecting the first portion and the step of electrically connecting the third portion comprise concurrently carrying out both the step of electrically connecting the first portion and the step of electrically connecting the third portion.
For example, in the case where both. the step of electrically connecting the first portion (i.e., the first connecting step) and the step of electrically connecting the third portion (i.e., the second connecting step) are done by soldering, those two steps may be carried out concurrently. In this case, the total number of steps can be reduced, that is, the total time needed to carry out all the steps can be reduced. Thus, the photovoltaic panel can be produced at reduced cost. For example, after the hole forming step, the fitting step, and the removing step are carried out, the core portion may be connected to the second electrode plate while the shell portion is connected to the first electrode plate. For example, each photovoltaic element which is being heated is pressed against the second electrode plate. In this manner, the shell portion is electrically connected to the first electrode plate, and concurrently the core portion is electrically connected to the second electrode plate. However, the first and second connecting steps may be carried out separately from each other. For example, the hole forming step, the fitting step, the first connecting step, the removing step, and the second connecting step may be carried out in this order. More specifically described, after each photovoltaic element is fitted in the hole formed in the first electrode plate, the shell of the each element is connected to the first electrode plate, and then the removing step and the second connecting step are carried out. If in each of the first and second connecting steps, the electrical connection is done by soldering, it is preferred that the melting point of the solder used in the second connecting step be lower than that of the solder used in the first connecting step. Since the solder used in the second connecting step is heated to a temperature lower than that to which the solder used in the first connecting step is heated, the photovoltaic elements which have been connected to the first electrode plate in the first connecting step are effectively prevented from floating on the solder which would otherwise be molten again.
(11) According to an eleventh feature of the present invention that includes any one of the first to tenth features (1) to (10), at least one of the step of electrically connecting the first portion and the step of electrically connecting the third portion comprises pressing the each photovoltaic element against a corresponding one of the first electrode plate and the second electrode plate.
It is preferred that the soldering be carried out while each photovoltaic element is pressed against the first and/or second electrode plates. However, this is not essentially required. The eleventh feature (1) just requires that the pressing be done during at least a portion of a time duration in which the soldering is carried out.
(12) According to a twelfth feature of the present invention, there is provided a method of producing a photovoltaic panel, comprising the steps of forming a plurality of holes through a thickness of a first electrode plate including an electrically insulating layer and an electrically conductive layer which are superposed on each other, fitting, in the plurality of holes, a plurality of photovoltaic elements, respectively, each of which has a P-N junction between a core portion thereof and a shell portion thereof, removing a first portion of the shell portion of the each photovoltaic element that is located on the side of the insulating layer of the first electrode plate, so that a second portion of the core portion of the each photovoltaic element that corresponds to the first portion of the shell portion is exposed, electrically connecting a third portion of the shell portion of the each photovoltaic element to the conductive layer of the first electrode plate, and electrically connecting the exposed, second portion of the core portion of the each photovoltaic element to a second electrode plate.
In the present photovoltaic-panel producing method, the plurality of holes are formed in the first electrode plate including the insulating layer and the conductive layer, and the photovoltaic elements are fitted in the holes, respectively. The present method employs the first electrode plate which has the insulating layer, and no new insulating layer is formed on the exposed core portion of each photovoltaic element. Therefore, the present method does not need a polishing step for polishing and removing a portion of the insulating layer before the core portion is electrically connected to the second electrode plate. Thus, since the total number of steps of the present method can be reduced as compared with that of the conventional producing method, the present method can produce the photovoltaic panel at reduced cost.
The producing method according to the twelfth feature (12) may employ any one of the above-described first to eleventh technical features (1) to (11).
(13) According to a thirteenth feature of the present invention, there is provided a photovoltaic panel comprising a first electrode plate having a plurality of holes; a plurality of photovoltaic elements each of which has a P-N junction between a core portion thereof and a shell portion thereof covering a first portion of the core portion, and which are fitted in the plurality of holes, respectively, such that the shell portion of each of the photovoltaic elements is electrically connected to the first electrode plate; and a second electrode plate which is electrically connected to a second portion of the core portion of the each photovoltaic element that is opposite to the shell portion thereof and is not covered by the shell portion, wherein at least one of the shell portion, and the second portion of the core portion, of the each photovoltaic element is electrically connected, by soldering, with a solder, to a corresponding one of the first electrode plate and the second electrode plate.
(14) According to a fourteenth feature of the present invention that includes the thirteenth feature (13), the each photovoltaic element is formed from a silicon-based material and additionally includes a to-be-soldered layer which is formed from a material having a good capability to be connected to both the solder and the silicon-based material, so that the to-be-soldered layer covers the at least one of the shell portion and the second portion of the core portion and the at least one of the shell portion and the second portion of the core portion is electrically connected via the to-be-soldered layer to the corresponding one of the first electrode plate and the second electrode plate.
In the present photovoltaic panel, each photovoltaic element is connected, by soldering, to the first and/or second electrode plates via the to-be-soldered layer.
(15) According to a fifteenth feature of the present invention that includes the fourteenth feature (14), the material from which the to-be-soldered layer is formed comprises at least one of nickel, nickel alloys, titanium, copper, cobalt, palladium, gold, and silver.
It is preferred that the to-be-soldered layer be formed, by plating, of a nickel alloy. The nickel alloy may be selected from nickel-cobalt-phosphorus alloy (Nixe2x80x94Coxe2x80x94P), nickel-iron-phosphorus alloy (Nixe2x80x94Fexe2x80x94P), nickel-tungsten-phosphorus alloy (Nixe2x80x94Wxe2x80x94P), nickel-rhenium-phosphorus alloy (Nixe2x80x94Rexe2x80x94P), nickel-palladium-phosphorus alloy (Nixe2x80x94Pdxe2x80x94P), nickel-copper-phosphorus (Nixe2x80x94Cuxe2x80x94P), nickel-tin-phosphorus alloy (Nixe2x80x94Snxe2x80x94P), nickel-zinc-phosphorus alloy (Nixe2x80x94Znxe2x80x94P), nickel-manganese-phosphorus alloy (Nixe2x80x94Mnxe2x80x94P), nickel-rhenium-tungsten-phosphorus alloy (Nixe2x80x94Rexe2x80x94Wxe2x80x94P), nickel-rhenium-tin-phosphorus alloy (Nixe2x80x94Rexe2x80x94Snxe2x80x94P), and nickel-rhenium-zinc-phosphorus alloy (Nixe2x80x94Rexe2x80x94Znxe2x80x94P).
(16) According to a sixteenth feature of the present invention that includes the fourteenth or fifteenth feature (14) or (15), at least one of the first electrode plate and the second electrode plate comprises an electrically insulating substrate and an electrically conductive, solder layer which coats at least a portion of one of opposite surfaces of the substrate.
The first and second electrode plates may, or may not, be identical with each other. Each electrode plate may be provided by the combination of a conductive layer and a solder layer coating one surface of the conductive layer (i.e., a one-conductive-layer structure); the combination of an insulating layer, a conductive layer, and a solder layer coating one surface of the conductive layer (i.e., a one-conductive-layer-and-one-insulating-layer structure); or the combination of an insulating layer and a solder layer directly coating one surface of the insulating layer. In the last case, the solder layer functions as a conductive layer. Each conductive layer may be provided by a copper or nickel sheet which is coated with a nickel plating. Each insulating layer may be formed of a synthetic resin such as a phenol resin or a glass fiber reinforced plastics. Thus, the first electrode plate can be called as a ball arranging substrate. In addition, at least one of the first and second electrode plates may be provided by a printed wiring board. Since generally a printed wiring board includes a conductive layer, it can be used as it is.
(17) According to a seventeenth feature of the present invention that includes any one of the thirteenth to sixteenth features (13) to (16), the photovoltaic panel further comprises an annular electrical insulator which covers an annular portion of the core portion of the each photovoltaic element that is located between the first and second portions thereof.
Since the annular electrical insulator covers the annular portion of the core portion of each photovoltaic element that is located between the first and second portions thereof that are eventually connected to the first and second electrode plates, respectively, the first and second electrode plates can be reliably insulated from each other.
(18) According to an eighteenth feature of the present invention that includes any one of the thirteenth to seventeenth features (13) to (17), the first electrode plate comprises an electrically insulating substrate and an electrically conductive, solder layer which coats at least a portion of one of opposite surfaces of the substrate, and wherein an area of an opening of each of the holes that opens on the side of the one surface of the substrate is smaller than an area of an opening of the each hole that opens on the side of the other surface of the substrate.
(19) According to a nineteenth feature of the present invention, there is provided a photovoltaic panel comprising a first electrode plate including an electrically insulating layer and a first electrically conductive layer which are superposed on each other, the first electrode plate having a plurality of holes formed through a thickness thereof; a plurality of photovoltaic elements each of which has a P-N junction between a core portion thereof and a shell portion thereof covering at least a first portion of the core portion that is located on the side of the first conductive layer of the first electrode plate, and which are fitted in the plurality of holes, respectively, such that the shell portion of each of the photovoltaic elements is electrically connected to the first electrode plate; and a second electrode plate including a second electrically conductive layer which is electrically connected to a second portion of the core portion of the each photovoltaic element that is located on the side of the insulating layer of the first electrode plate and is not covered by the shell portion.
In the present photovoltaic panel, the first electrode plate including the insulating layer and the first conductive layer has the plurality of holes, and the photovoltaic elements are fitted in the holes, respectively. One half portion of the core portion of each photovoltaic element that is located on the side of the first conductive layer of the first electrode plate is covered by the shell portion, and at least a portion of the other half portion of the core portion that is located on the side of the insulating layer is exposed and is electrically connected to the second electrode plate. Upon incidence of a light to the shell portion on the side of the first conductive layer, an electric current flows between the first and second conductive layers via an external resistor.
The present photovoltaic panel may employ any one of the above-described thirteenth to eighteenth features (13) to (18).
(20) According to a twentieth feature of the present invention that includes the nineteenth feature (19), the photovoltaic panel further comprises an annular space which surrounds an annular portion of the core portion of the each photovoltaic element that is located between the first and second portions thereof.
In the present photovoltaic panel, the annular space functions as an insulator. This insulator is not formed by chemical treatment, and the annular space is not filled with an insulating material in a molten state. Thus, the air present in the annular space functions as the insulator.